In the production of optical components, recording media, semiconductor devices, etc., as a method for forming a fine pattern in a short time, a method for forming a fine pattern on a surface of a substrate (nanoimprint method) is known wherein a mold having on its surface a reverse pattern of such a fine pattern, is pressed to a photocurable composition placed on the surface of a substrate, and the photocurable composition is irradiated with light to cure the photocurable composition thereby to form a fine pattern on the surface of the substrate (Patent Documents 1 and 2).
However, in such a method, the cured product of the photocurable composition adheres to the mold, whereby it is difficult to separate the cured product from the mold. Therefore, it is necessary to apply a release agent to the surface of the mold or to use a photocurable-composition whereby it is possible to form a cured product having a good release property.
However, when a release agent is used, it becomes difficult to precisely transfer the reverse pattern of the mold due to the film thickness of the release agent itself, uneven application of the release agent, etc.
On the other hand, as a photocurable composition capable of forming a cured product having a good release property, the following one has been proposed.
(1) A photocurable composition comprising a fluorinated monomer, a monomer containing no fluorine, a fluorinated surfactant or fluorinated polymer, and a photopolymerization initiator (Patent Document 3).
However, when the photocurable composition (1) is used, it is difficult to obtain a cured product having a moderate flexibility (hardness: 50 to 85). Therefore, when a mold is separated from the cured product, the cured product having a fine pattern formed is likely to be broken, and thus the transferring property sometimes deteriorates.
As a photocurable composition which is capable of forming a cured product having flexibility and which is excellent in transferring property, the following one has been proposed.
(2) A photocurable composition comprising a urethane (meth)acrylate oligomer, a bifunctional monomer and a photopolymerization initiator (Patent Document 4).
However, since the cured product of the photocurable composition (2) has a high adhesion, it has an insufficient release property.
Further, the nanoimprint method includes a step of placing a photocurable composition on a surface of a substrate or a surface of a mold. Accordingly, the photocurable composition is required to have characteristics such that it is capable of being applied without a special operation and does not flow off from the surface of the substrate or the mold. Therefore, it is also important for the photocurable composition used for the nanoimprint method that its viscosity can be properly adjusted.